Improving Remote Sensing of Aerosol Microphysical Properties by Near‐Infrared Polarimetric Measurements Over Vegetated Land: Information Content Analysis

Abstract

While polarimetric measurements contain valuable information regarding aerosol microphysical properties, polarization data in the near‐infrared (NIR) bands have not been widely utilized. This paper evaluates whether the aerosol property information contents from single‐viewing satellite polarimetric measurements at 1,610 and 2,250 nm can be used to improve the retrieval of aerosol parameters over vegetated land, in combination with shorter‐wavelength bands (490, 670, and 870 nm). The a priori information and errors for the analysis are derived by assuming that the surface reflectance at visible wavelengths can be derived from the top of atmosphere at 2,250 nm. The information content in the synthetic data set is investigated for 10 aerosol parameters characterizing the columnar aerosol volumes ( V0f and V0c), particle size distributions ( refff, vefff, reffc, and veffc), and refractive indices ( mrf, mif, mrc, and mic) for the fine‐ and coarse‐mode aerosol models, respectively, and one parameter C characterizing the surface polarization. The results indicate that the degrees of freedom for signal can be increased by at least 2 with the addition of NIR measurements and that one to three additional parameters could be further retrieved with significantly decreased uncertainties. In addition, the 1,610 nm band is necessary for the simultaneous retrieval of V0f, mrf, and refff for the fine mode dominated aerosols, while the 1,610 and 2,250 nm bands are both indispensable for retrieving V0f, V0c, mrc, refff, and reffc in tandem for the coarse mode dominated aerosols. The analysis also reveals that C could be further retrieved by including scalar radiance and that measurement errors have significantly larger influences on the retrieval uncertainties than model errors.

Study on the spectral reconstruction of typical surface types based on spectral library and principal component analysis

“…In order to test the spectral reconstruction based on the linear combination model, the surface information of four common bands for satellite remote sensing, including 490, 555, 670 and 865 nm [16][17][18][19][20][21] , are used to the spectral reconstruction. Figure 6 shows the scatter plots of the reconstructed and true surface reflectance at 440 nm, and Figure 7 shows the reconstructed reflectance results at 810nm.…”

“…Principal component analysis (PCA) has been widely used in the study of spectral compression and reconstruction, in which, a spectral data set can be decomposed into the linear combinations of several main spectral components [9][10][11][12] . Previous studies have shown that in the visible range of 400-700 nm, the first six principal components (PCs) can meet the needs of spectral reconstruction [13][14] ; while for the wavelength range of 400-2500 nm, [12][13][14][15][16][17][18][19][20] PCs are needed to reconstruct the vegetated surface spectra 15 .…”

Retrieval of Aerosol Microphysical Properties Based on the Optimal Estimation Method: Information Content Analysis for Satellite Polarimetric Remote Sensing Measurements

“…The closer the value of :,: to 1, the better the retrieval of parameter x : . Besides, as long as the DFS result :,: > 0.5 , we assume that the retrieval of parameter x : could be carried out (Hou et al, 2018).…”

“…In addation, the setting of a priori errors of measurements, aerosol models and each retrieved parameter are same as the parameters setting in the work of Hou et al (2017Hou et al ( , 2018, thus the detailed results are not listed here due to space limitations.…”

“…In both cases, the aerosols are mixed with different relative percentages of fine-and coarse-mode particles, in which the fine-mode fraction of columnar volume concentration FMF † corresponds to 0.8 and 0.2, respectively. Besides, the parameters of particle size distribution and complex refractive index for both fine and coarse mode aerosols are taken from the work of Hou et al (2017Hou et al ( , 2018, based on the ground measurements of Sun-sky radiometer observation network (SONET) . Figure 1 shows the scattering phase function ( ** ) and the polarized phase function (-*+ ) for the fine-mode and coarse-mode aerosol scenarios respectively.…”